<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="vue.js"></script>
</head>
<body>
    <div id='app'>
        <!-- input中的v-mode1用于在表单控件元素上创建双向数据绑定 -->
        <input type="text" v-model="cityName">
    </div>
    <script>
        var vm = new Vue({
            el: '#app',
            data:{
                cityName:'shanghai'
            },
            // 使用watch监听cityName变化
            watch:{
                cityName (newName, oldName) {
                    console.log(newName, oldName)
                }
            }
        })
    </script>
</body>
</html>